NOAA/WDS Paleoclimatology - Malevich - Dalton Reservoir Update - PIPO - ITRDB CA676

This work presents the first tree-ring reconstructions of hydroclimate for the Upper Klamath River basin, which stretches from northern California into southern Oregon. The extended record provides a centuries-long perspective on the region’s hydroclimatic variability and context for water-related political issues that have erupted in recent years. Reconstructions of water-year precipitation for Klamath Falls, Oregon (extending 1564-2004 and 1000-2010 CE) were developed to compare past drought severity with drought severity of the instrumental record (extending 1896-2011). The reconstructions suggest that variability exhibited during the instrumental period captures extremes of moderate-to-long-duration (6-, 10-, and 20-year) droughts, but not of short (single-year and 3-year) and very long (50-year) droughts, which were more severe during the 11th-13th centuries. The late-16th-century “mega drought” is present in the Klamath River basin, though with less strength than in the neighboring Sacramento River basin. Cool-season storm tracks appear to be a direct driver of hydroclimatic variability, leading to instances of see-saw like relationships with neighboring regions, such as in the mid-14th century. In contrast, the larger area of drought in the 12th century is suggestive of a long-term northward shift in cool-season storm tracks.

本研究首次完成了克拉马斯河上游流域的水文气候（hydroclimate）树轮重建（tree-ring reconstructions）序列，该流域北起加利福尼亚州北部，延伸至俄勒冈州南部。本次构建的扩展气候序列，为该区域的百年尺度水文气候变异性研究提供了长时序视角，同时也为近年来爆发的涉水政治议题提供了历史背景参照。针对俄勒冈州克拉马斯福尔斯地区的水文年降水量（water-year precipitation）重建序列（时间跨度分别为1564–2004年与1000–2010年），旨在将历史干旱严重程度与器测记录（instrumental record，1896–2011年）中的干旱严重程度进行对比分析。重建结果表明，器测时期所记录的气候变异性涵盖了中长历时（6年、10年及20年）干旱的极端事件，但未涵盖短历时（单年与3年）及超长历时（50年）干旱——后者在11至13世纪的干旱强度更为显著。16世纪晚期的‘特大干旱（mega drought）’事件同样出现在克拉马斯河流域，但其强度弱于邻近的萨克拉门托河流域。冷季风暴路径（cool-season storm tracks）似乎是该区域水文气候变异性的直接驱动因子，这使得本区域与邻近区域呈现出类似跷跷板式的气候关系，例如14世纪中期的情况。与之形成对照的是，12世纪出现的大范围干旱现象，暗示冷季风暴路径发生了长期北移。